Ординатура / Офтальмология / Английские материалы / Essentials in Ophthalmology Pediatric Ophthalmology Neuro-Ophthalmology Genetics_Lorenz, Borruat_2008

tients with maculopathies (Altpeter et al. 2000). Patients who had good attentional capabilities in the lower visual field showed a fixation locus below the scotoma. If attentional capabilities were reduced in the lower visual field, these patients preferred a fixation locus left or right of the scotoma, since attentional capability was generally better on the horizontal meridian. There are some indications that these attentional mechanisms can be improved by training. Therefore, it should be possible to detect locations with reduced attentional capabilities before eccentric fixation develops and to provide goal-directed training for those patients who are at risk of developing an unfavorable PRL.

Summary for the Clinician

■Optic neuropathies can cause various field defects.

■It is crucial that patients with a central scotoma use an eccentric fixation locus, the reduced resolution of which can be compensated for by text magnification.

■Stable eccentric fixation can be determined by the position of the blind spot in the perimetry, as it is shifted together with the scotoma.

■Ring scotomas and arcuate scotomas can lead to an insufficient size of the reading visual field. In these cases, one may have to wait for the central fields of both eyes to develop absolute scotomas, so that eccentric fixation can develop.

■In constricted concentric fields, the central seeing island can be too small for reading. Contrast enhancement with very small letter size can be helpful.

blind temporal hemifields, resulting in a completely blind triangular area posterior to fixation (Kirkham 1972).

Inpatientswithbitemporalhemianopiathereis no normal overlap of the nasal visual fields, which prevents fusion. Therefore, pre-existing phorias easily decompensate to tropias, thus causing the “hemifieldslidephenomenon”(Fig. 17.5).Incases of pre-existing esophoria or intermittent esotropia, patients will experience a separation of the nasal hemifields, causing a blind area in the center of the field. Patients with pre-existing exophoria or intermittent exotropia will have an overlap of the two hemifields, and patients with pre-ex- isting hyperdeviations will experience a vertical separation of the images crossing the vertical meridian (Kirkham 1972). This hemifield slide phenomenon has a severe impact on everyday life by causing difficulties with reading or separation of a sequence of optotypes, which can be specially disabling in the case of long numbers, for example a banker does not know if an account has 500 000 Euro or 5 000 or maybe even 5 millions (see Fig. 17.5). It is important that patients be made aware of this phenomenon to guard against misinterpretations of reading material. Monocular reading can be helpful in these cases.

Summary for the Clinician

■Bitemporal hemianopia causes problems with spatial orientation due to the constricted temporal fields (“blinkers visual fields”).

■The lack of overlap of the nasal fields can cause the hemifield slide phenomenon with severe confusion during reading.

■Patients have to be made aware of this phenomenon to protect themselves from misinterpretations.

17.3.2 Optic Chiasmal Syndromes

Other disturbances have to be considered in addition to the well-known orientation impairment caused by limited temporal fields: one type affects depth perception, which leads to difficulties with near-distance tasks such as sewing, threading needles or using precision instruments. In these cases, convergence causes crossing of the two

17.3.3Suprachiasmatic Lesions of the Visual Pathways

Visual field defects are typified by the location of their causative lesion. In suprachiasmatic lesions the visual field defect is homonymous, mostly an upper or lower quadrant, or a complete hemiano-

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Fig. 17.5.  Hemifield slide phenomenon in bitemporal hemianopia: absence of the normal overlap of the nasal visual fields prevents fusion and causes overlap of the two hemifields in exodeviation, separation of the two hemifields in esodeviation and vertical separation in hyperdeviation (after Kerkham 1972). This hemifield slide phenomenon causes severe problems with reading words and especially long numbers (see text)

pia with macular splitting. In cases with sparing of the occipital pole there is a sparing of 2°–5° in the blind hemifield along the horizontal meridian, called macular sparing (Trauzettel-Klosinski and Reinhard 1998; Reinhard and TrauzettelKlosinski 2003).

Alternatively, in cases showing an isolated 17 lesion of the occipital pole, a small paracentral

homonymous defect can result.

The pathogenesis of homonymous field defects is mostly ischemia (59%–89%), less often tumors or hemorrhage (3%–23%), surgery and trauma (2%–14%), and others (4%–7%) (summarized results of several studies in Kölmel 1988; Trobe et al. 1973; Zihl and von Cramon 1986; Zhang et al. 2006). In the majority of cases the lesion is located in the occipital lobe (45%) and in the optic radiation (32%) (Zhang et al. 2006).

17.3.3.1Hemianopic Reading Disorder

Homonymous hemianopia causes severe reading problems, since in complete hemiano-

pia half of the reading visual field is obscured (Fig. 17.6a; 1).

If there is a macular sparing, the reading visual field can be preserved and reading can be normal, despite the fact that there is a large field defect in the remaining hemianopic side (Fig. 17.6a; 2). Then again, a small paracentral homonymous scotoma, which occurs in cases with an isolated lesion of the occipital pole, causes severe problems with reading, because it covers half of the reading visual field (Fig. 17.6a; 3). These small paracentral scotomas are easily overlooked in automated perimetry if the grid of the test program is not dense enough. Hence, an especially dense grid should be chosen, while manual perimetry allows for a specific search for small scotomas.

The severity of the reading problems in hemianopia not only depends on the distance of the visual field defect from the center, i.e., the size of the reading visual field, but is also influenced by the side of the defect. In left to right readers a hemianopic field defect to the right side is extremely impairing, because the visual field defect is in the reading direction. Figure 17.7 shows on the left the eye movements for a normal subject; in the middle, for a patient with right hemianopia. This patient needs many more saccades per line and makes a lot of regressions to get through the line. A patient with left hemianopia (right) gets through the line quite easily, but has difficulties in finding the beginning of the next line, which is shown by the additional steps during the return sweep.

Patients with hemianopia can learn compensating strategies: they perform frequent eye movements towards the blind hemifield, i.e., explorative saccades to increase the field of gaze. In early stages they often show a staircase pattern, and later an overshoot or predictive strategy (Meienberg et al. 1981).

Another compensating strategy can be eccentric fixation in cases with macular splitting (Fig. 17.6b). The patient in Fig. 17.6b uses a slightly eccentric retinal locus for fixation, which causes little sacrifice of visual acuity, and creates an extended perceptual span along the vertical midline that is crucial for fluent reading. Eccentric fixation causes a shift of the field defect towards the hemianopic side in conventional perimetry, which can be misinterpreted as improvement of the visual field. This process indicates a

high cortical plasticity, because the new eccentric fixation locus is not only used as the new center of the visual field, but also as the new center of the coordinates of the reading eye movements, which means a shift of the sensory and motor reference. It should be emphasized that these pa-

tients have intact foveal vision and are still able to use an eccentric fixation locus if it is required by the task. When visual acuity is tested, they use their foveola for highest resolution (TrauzettelKlosinski 1997).

17.3.3.2Hemianopic Orientation Disorder

Patients with hemianopia are severely impaired in spatial orientation. They often bump into obstacles on the hemianopic side and have to learn to perform explorative saccades towards the

17 hemianopic side, which many patients start doing spontaneously. In conventional perimetry, this behavior shifts the field defect to the blind side and this is often misinterpreted as an improvement of the visual field.

Summary for the Clinician

■Hemianopic reading disorder is characterized by a reduced size of the reading visual field.

■If there is a macular sparing of 2º–5°, reading is normal, otherwise it is severely disturbed.

Summary for the Clinician

■Patients with right-sided hemianopia are more impaired than those with a leftsided hemianopia, because the field defect is in the reading direction. They have to make many saccades to get through a line of text.

■Patients with left-sided hemianopia have difficulties finding the beginning of the next line.

■Small paracentral homonymous defects can easily be overlooked in routine perimetry. Apply manual perimetry or a dense grid in automated procedures!

■Eccentric fixation can be helpful to create a small perceptual span along the vertical midline.

■Spatial orientation problems caused by homonymous hemianopia can be improved by frequent saccades towards the blind hemifield.

17.3.4 Cortical Visual Impairment

Cortical visual impairment (CVI) is an underestimated diagnosis. Many causes exist, but the most common one is hypoxic-ischemic brain injury in preterm and term infants (Dutton and Jacobson 2001; Good et al. 2001; Hoyt 2003). Equally important and often ignored is the fact that quite different patterns of brain damage can result from hypoxic-ischaemic insults depending on the child’s age, as well as the location, severity and duration of hypoxia. A certain degree of recovery occurs in cases of striate cortex injury, but not in those of periventricular leucomalacia (Hoyt 2003).

The main problem is the quantitative assessment of residual visual function, which is hindered by reduced compliance and the fact that many of these children have multiple disabilities. Measuring visual acuity is not sufficient, and there is a need for more specific tests to improve functional diagnostics in regard to specific rehabilitation programs. Many children do not only have reduced visual acuity, but also visual field defects, strabismus, nystagmus, decreased contrast sensitivity, and oculomotor disorders. Often they have difficulties in information processing and integration, sometimes specific agnosias; for example, central achromatopsia (color desaturation), prosopagnosia ( problems in recognizing faces), cerebral akinetopsia (inability to perceive moving targets), simultanagnosia ( inability to focus on more than one visual object at a time), astereocognosis (difficulties with depth perception), and topographic agnosia (problems with orientation) (Good et al. 2001).

Early assessment is critical. Visual and cognitive development are closely related (Good et al. 2001). For children with CVI, a simplified visual environment is more beneficial than diverse stimulation, because it forces them to focus attention on a particular visual stimulus (BakerNobles and Rutherford 1995; Good et al. 2001). Color, high contrast, and use of motion may facilitate recognition of an object (Baker-Nobles and Rutherford 1995).

17.4Diagnostic Procedures

to Examine Reading Ability

•Specific diagnostics in regard to the existing and the potential reading ability is the basis for rehabilitation programs.

•Exact determination of the refractive error is necessary because insufficient corrections would be enhanced while using magnifying visual aids.

•Visual acuity for distance: if visual acuity ≤0.1, the measurement should be performed by ETDRS charts, because they allow more steps in the low vision range by reducing the distance.

•Near visual acuity and range of accommodation.

•The most important examination is determination of the magnification requirement. This tells immediately whether magnification is effective at all and, if so, how much magnification is necessary. Different charts are available in different languages: MN-Read charts and Reading Navigator in many languages, Zeiss charts, Radner charts in German, and, for children, Lea Symbols. The smallest print size that can be read fluently corresponds to the magnification need. Even though mathematically there is a reciprocal relationship between visual acuity and magnification need, in reality there is often a discrepancy (for example, in a ring scotoma with good visual acuity versus high magnification need, see above). Therefore, measurement of magnification need is crucial for the future visual aid.

•Examination of parafoveal contrast sensitivity: for determination of potential reading ability, also for assessment of eccentric retinal areas that are suitable for reading, the Macular Mapping Test (MacKeben et al. 1999; Trauzettel-Klosinski et al. 2003) is a valuable method.

•Reading speed should be determined by reading a text passage aloud. A whole text passage is preferable to a single sentence for more accurate speed measurement and judgment of fluency and mistakes. For this test, a newly developed set of equivalent texts in different languages is available, which can also be used for repeated testing. The texts are com-

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Visual aids for distance are telescopes, so-called monoculars, which are available in different magnification steps (Fig. 17.8; 13). They enable

an ultrasonic device for detecting obstacles can be an additional help.

17.5.3 Training

17.5.3.1Training for Patients with Circumscribed Scotomas in the Central Field

Training in operating the visual aids is crucial. Patients need to learn that they can use only a limited distance to the reading material when they use a magnifying spectacle, and that they can benefit from moving the text in front of their

eyes when a very short reading distance is used. A book rest is helpful in maintaining an ergonomically good posture for longer periods of reading.

Learning compensating strategies will become increasingly important: on the one hand, this could be training to use the best retinal locus for reading; on the other hand it could be specific reading training, which can widen the perceptual span and improve the saccadic strategy. Regarding eccentric fixation training, several studies have reported positive results (Frennesson et al. 1995; Nilsson.et al. 2003; Watson 2002).

17.5.3.2Training for Patients with Homonymous Field Defects

17.5.3.2.1The Controversy about Training in Hemianopia

The following issues with training studies should be considered (see also Trobe et al. 2005):

•Specificity: spontaneous recovery can occur, especially in the first few months. Further, a control group is crucial to verify any improvement.

•Reliability: the way in which the training effect is assessed is important, i.e., whether appropriate methods are used to detect any changes.

•Aim: another important point is how improvement is defined. From what degree of change is an improvement clinically relevant?

Spontaneous recovery can occur at a range of 7%–53 %, depending on the definition of improvement and the cohort of observed patients (Kölmel 1988; Trobe et al. 1973; Zihl and von Cramon 1986). Studies in which only behavioral parameters were judged showed an improvement of 60% to over 80% (Hier et al. 1983).

The problems of conventional perimetry are:

(1) limited spatial resolution, (2) scattering light of the stimulus, and (3) insufficient fixation control. In contrast, the scanning laser ophthalmoscope (SLO) presents an inverse stimulus without light scattering. Additionally, the SLO allows simultaneous fixation control during stimulus presentation. The vertical visual field border depends essentially on the quality of fixation: if fixation is stable and central, there is good agreement between conventional perimetry and SLO perimetry. If fixation is unstable or eccentric, the visual field border is shifted towards the hemianopic side in conventional perimetry, which can mimic an improvement of the visual field defect (Trauzet- tel-Klosinski and Reinhard 1998). Therefore, for judging the visual field border, it is necessary also in conventional perimetry to control fixation and to be aware of shifts by eye movements.

There are two different approaches and goals for training: restitution and compensation. In

17.5  Rehabilitation Programs 315

former studies with restitution training the stimulation was performed at the border of the hemianopic field defect. Here the risk is stray light and eye movements towards the stimulus (Kasten et al. 1998; Zihl and von Cramon 1979). The goal of restitution training is to re-activate incompletely damaged neurons in the blind field and to enlarge the visual fields by stimulation at the border of the field defect. Perimetric targets were presented at threshold along the visual field border (Zihl and von Cramon 1979). The authors reported an improvement of the visual field up to 40º. In a later study (Balliet et al. 1985) these results could not be confirmed. In the study by Kasten et al. (1998) visual restitution training (VRT) was performed by presenting perimetric targets above threshold along the visual field border. The authors described an extension of the seeing hemifield by approximately 5º. Then againhand, Reinhard et al. (2005) performed an SLO study before and after VRT using fundus perimetry with simultaneous fixation control and a grid of 0.5° spatial resolution horizontally and 1° vertically in the 10° visual field. In this case, no improvement of the visual field could be found. Also in a study with conventional perimetry no relevant effect after VRT was described (Schreiber et al. 2006).

The restitution training studies present the stimulus along the vertical field border, which should be differentiated from another kind of stimulation performed in the periphery of the visual field and where residual vision was described in a few, well-trained patients. This “blindsight” is an unconscious perception of visual stimuli via the superior colliculus to extrastriate regions without activation of V1 (Pöppel et al. 1975; Vanni et al. 2001; Weiskrantz 2004). It is an open question whether training can improve this kind of residual vision to a level that is relevant for everyday life.

Compensating training assumes a stable border between the seeing and non-seeing hemifields. The goal here is to enlarge the field of gaze by frequent eye movements into the blind hemifield by shifting attention to the blind side. This kind of training can be effective at improving the utilization of the blind hemifield (Kerkhoff et al. 1992; Pambakian et al. 2004).

Optical aids are controversial; mirrors and prisms were described as beneficial in single

316Rehabilitation in Neuroophthalmology

cases but were not really adopted by large patient groups, because most patients are confused by the double images and the resulting interference with spatial orientation.

17.5.3.2.2Recommended Methods

•Training to shift visual attention towards the blind hemifield

•Compensatory search strategies

- Frequent saccades towards the hemianopic side for enlargement of the saccadic search field

- Specific visual search to systematize search strategies

•Utilization of information from the blind hemifield to the seeing one (parts of objects, stray light, reflections)

•Training in the real-life environment of the patient

•Training with an orientation and mobility trainer

•Specific explorative training at a monitor or on a sheet of paper (Kerkhoff et al.1992; Pambakian et al. 2004; Zihl 1995), which was reported to be beneficial, but none of these studies included a control group

Approaches to improve the hemianopic reading disorder include:

•Training to improve orientation on the page, visual and tactile tools (bar magnifier with underlining, ruler or forefinger are helpful)

•Special reading training with scrolling text (Kerkhoff et al. 1992; Zihl et al. 1984)

•Moving the text into a vertical or diagonal position may be beneficial, but has not been tested in a larger patient group

•Another approach can be eccentric fixation to enlarge the perceptual span

A general recommendation is to explain to the patient and relatives the special nature of the visual impairment in detail and to inform them that he/ she is not allowed to drive. (This law is valid in Europe and some of the states in the USA, where exceptions exist for getting a restricted license.)

Summary for the Clinician

■Training is important for optimizing the use of residual vision.

■Trainingdeficit. has to be specific to the visual

■The value of training should be related to its relevance for everyday life.

17.5.4Counseling Regarding Public Support

When the procedure of selection, adaptation, and coordination of visual aids and of training is completed, consideration should be given to how the visual impairment will affect the patient’s education, profession, leisure time and, in elderly patients, the ability to maintain an independent life style. Self-help organizations, and help from neighbors and other social services can be very valuable and can help to maintain a patient’s independence. Sometimes it is necessary to include a psycho-social consultation, especially if the eye disease additionally causes depression in elderly patients. In addition, it is important to find out whether, and to what degree, the patient can expect receiving support from government agencies and institutions, which may vary between different countries.

17.6 Summary and Conclusions

The ability to read can be regained if foveal function is lost and fixation is eccentric. The reduced spatial resolution of retinal areas outside the fovea can be compensated by magnification of the text. If the fovea is intact (for example, in patients with a ring scotoma or hemianopia) and fixation is central, the problem is the limited size of the reading visual field. Here, eccentric fixation has to be waited for or trained, or the print size has to be kept very small in conjunction with contrast enhancement. For hemianopic patients, diagonal or vertical text orientation might be helpful, and help via tactile or visual orientation on the page can be recommended. The precondition for reading is therefore sufficient spatial resolution of the retinal area used for reading as well as sufficient